In the manufacture of a printed circuit board (PCB), it is necessary to drill holes in the PCB. When a PCB is made, it is rarely made in quantities of just one or two. Usually, it is made in large production runs of several hundred. When that occurs, it is important to drill all of them in the same fashion. Accordingly, the PCB will be first plated and then the etching will occur to locate the pads and leads on the PCB. This is true whether it is plated on one or both sides. Thereafter, holes are drilled through the PCB and the holes must be aligned with the leads and pads on previously formed on the PCB. This often requires that several of the PCB""s be stacked together. Depending on thickness, it is possible to drill through at least two which are stacked, and it is often possible to drill through 10 or perhaps 20 depending on the length of the drill and the thickness of the stack. As the hole gets smaller, the number of stacked PCB""s typically is reduced because the drill bit gets shorter.
It is difficult to make a very fine gauge drill bit of great length to drill through a large number of stacked PCB""s.
The present disclosure is directed to a PCB drill bit which is particularly improved and which provides an improved drilling process. Accordingly, after drilling, the holes have highly defined circular edges with little fuzzing and sharp definition. Also, all of the holes in a stack will line up so that the stack is properly registered for the hole drilling process. To do this, the stack is held with some sort of registration device or edge. It is not uncommon to clamp perhaps 10 PCB""s in a stack with edge located clamp mechanisms.
The PCB drilling routine of the present disclosure is markedly enhanced by the treatment applied to the drill bits. This is a very useful approach for drilling relatively small holes. The present disclosure is especially useful for drill bits which form holes of the size of 1.50 mm and much smaller down to 0.10 mm. With holes that small, it is very difficult to accomplish repeated accurate drilling. When the PCB""s are assembled in a stack and are drilled by one bit passing through several of them, there is a production advantage obtained. The wear and tear on the drill bit is normally determined by the number of xe2x80x9chitsxe2x80x9d, not the number of PCB""s actually drilled. A hit is defined by the contact of the drill bit against a stack of PCB""s. If, to pick an example, four, six, or eight of the PCB""s are stacked then that number can be drilled with a single hit, meaning the drill bit contacts against the whole stack only once. That defines one hit, not the number of PCB""s in the stack.
In the past, a typical drill bit of the gauge mentioned above would suffice for about 2,000 hits and then would require repainting. In effect, this is resharpening at the tip of the drill bit. When repointed, it would last another 2,000 hits. Regular usage of the drill bit of the size range noted above would typically yield about 8,000 hits. This would require three separate repointing steps for the last three increments of 2,000 hits each. The drill bit would then be thrown away even though there might be some modest life left in it.
Using 1999 prices, assume that the drill bit costs three dollars. The hand labor and the work to put a new point on it typically is about three dollars, and can be even more. Thus, to get 8,000 hits, the cost of the drill bit will be as much as $12, taking into account the three trips to a repointing shop or facility. In a large production situation, the repainting is typically done nearby by skilled craftsman who are trained for that purpose. This might reduce the price of that step somewhat, but it still will be an expensive undertaking. Furthermore, the repainting and reinstallation takes some amount of time which has been treated as negligible in the above calculation, but it still may well increase significantly the cost of $12 to make 8,000 hits.
Through the use of the present disclosure, as will be explained, a single drill bit can be increased from about 8,000 hits to about 12,000 hits. Even more profoundly, however, the three trips from the PCB drill press to the repair shop for repainting are avoided. Accordingly, even if the drill bit costs more initially, say four dollars, it is much cheaper in the long run because the number of hits is much higher and the labor reduced in repointing (which requires dismounting, removal, later mounting and repetition thereof). This whole sequence is much easier to execute because repair of an individual drill bit is substantially eliminated.
The present disclosure is therefore able to provide a 50% increase in production for a single drill bit in the above mentioned example (an increase from 8,000 to 12,000 hits). While that 50% increase in production is obtained, the cost of the drill bit over the life of its use is reduced from about $12 to less than half of that.
The present disclosure is directed to an improved drill bit construction with a surface treatment applied to it. The surface treatment involves the initial manufacture of the drill bit with the sharp point as appropriate for the type of bit and the size of the bit. Treatment of teh surface of the drill bit can be accomplished simply by using the treatment materials discussed herein in lieu of cutting oil during the manufacture of the drill bit. The heat produced during the matal cutting is sufficient to bond the treament material to the newly cut surface of the drill bit. However, this method requires the cooperation of the manufacturer. Alternatively, after fabrication, the bit is prepared for the present enhancement which involves heating to a modest level. Then, it is dipped into a solvent which has a phosphorous surface treatment chemical in it. The solvent can be water-based, glycol based, or oil based. This surface treatment is applied to the drill bit, and especially in the portions of the drill bit which make contact with the PCB while drilling, and the compound provides a surface conversion or surface treatment of the drill bit material. All of the surface of the cutting portion is treated to a relatively thin depth of the material, in a more or less uniform layer. It is highly desirable that the treatment be applied to a depth of about one to five angstroms (xc3x85), and more particularly to a depth of about two xc3x85. As will be understood, surface layers that thin are difficult to measure. In effect, measurement of such a thin layer is accomplished best by inference. Preferably, the layer is formed by the indicated liquid base, and heat is used to drive off any surplus solvent. For instance, the drill bit can be initially heated to about 150xc2x0 F., dipped in the liquid base and then heated afterwards to something less than about 200xc2x0 F. In general terms, it is not necessary to heat it any hotter than about 175xc2x0 F. to 200xc2x0 F. to dry the treatment.
The foregoing application is achieved rather easily. While easily done, and easily adherent to the drill bit, it is effectively cured and forms a relatively tough, but slick surface. This slick surface seems to increase the life by reducing the wear and tear on the surface as a result of abrasion. While obviously the drill bit is many orders of magnitude harder than the PCB, there is eventually some wear and tear on the drill bit. In fact, it is commonplace to make the drill bit of tungsten alloys including tungsten carbide. Sometimes, the tungsten metal is alloyed with other metals so the finished drill bit is very hard. By contrast, the PCB can be effectively defined as a woven fiber glass fabric which is impregnated with elastomeric materials. Even the plastic of the PCB will wear out the hard metal alloy of the drill bit after much use.
In that context, a thin protective layer of about one to about five xc3x85 provides a high level of enhanced protection. The protection assures that the drill bit does not wear out as rapidly in the example given above, provides about a 50% increase in life in operation and achieves that at a 50% or more reduction in cost, taking into account the cost of repainting during use.
The present disclosure contemplates the protection of drill bits of different types of material. It is not uncommon to make such drill bits of tool steel. These drill bits have a specified dimensional stability and a fairly well predicted life. In addition, however, to tool steel, some of these drill bits are made of tungsten carbide particles. The tungsten carbide (WC is the chemical symbol) are made of such particles held together in a supportive alloy matrix. The alloy is primarily formed of cobalt along with several other alloy metals. Typically, the supportive matrix will comprise somewhere between five and twenty percent of the material with the remainder being formed of the WC particles. In the alloy itself, somewhere between 80 and 95 percent of it is normally cobalt (Co). The cobalt based alloy is a binding matrix which holds the WC particles together and provides dimensional stability and structural integrity. Moreover, the WC particles tend to be somewhat brittle and run the risk of breaking, but that is modified in the drill bit construction because the cobalt alloy matrix provides a yieldable material, which, in the composite structure, is relatively immune to shock loading. Therefore, for long production runs, the WC particles in the cobalt alloy matrix is the more desirable and higher grade drill bit. There is, however, a problem with the use of cobalt based drill bits. Cobalt interacts in a negative way with certain materials. In particular, cobalt is sensitive to silicon based materials and/or the solvents. Preferably, they simply do not make contact with the alloy because that will otherwise destroy the alloy. In the present disclosure, the protective material to be described first forms a conversion surface. Thereafter, a second layer may be formed comprising soluble silicates. That enables protection to be applied to tungsten carbide based drill bits. Moreover, that permits the protection to be placed in a fashion which assures long durability and the requisite protection of the drill bits when faced with long production runs.
The present disclosure is therefore summarized as a method of protecting drill bits and especially small diameter drill bits which are typically in the range of about 1.5 mm and smaller in diameter. It is intended to be used with such drill bits to provide a protective layer on the surface that is measured in the range of one or two xc3x85 for the preferred version and up to about five xc3x85. The treatment is applied by initially making the drill bit to the desired shape, then heating the drill bit and dipping it in a glycol base solution of phosphorous materials as defined below, and thereafter heating until the surface is dry. In testing subsequently with various test instruments, the surface shows a conversion surface containing phosphorous and appears to have a thickness in the range of about one or two angstroms. The finished drill bit then is ready for use. During use, it appears to run much cooler and holds a point and sharp edge longer. It is conjectured that the surface friction is reduced, thereby extending drill bit life.